Fluid clarification system and apparatus

ABSTRACT

A fluid clarification system and method is described in which fluid is passed through one or more settling compartments, each having a solids outlet at the base of the compartment. The base of each compartment includes inclined surfaces for guiding settled solids to the outlet. Also described is a polymer reaction trough including baffles to promote gentle mixing of inflow fluid with flocculant. The system is designed to reduce costs of transportation, flocculent, and solids handling. The system is preferably arranged to facilitate transport on a skid or trailer, while maximizing fluid handling capabilities and minimizing costs.

FIELD OF THE INVENTION

The present invention relates generally to the clarification of fluids.More particularly, the present invention relates to a system, method,and apparatus for separating suspended solids from a fluid stream toproduce a clarified fluid stream and a solids output stream.

BACKGROUND OF THE INVENTION

Downhole drilling operations are generally performed at remotelocations, and it is therefore desirable to reuse or recycle as manyresources as possible on-site to avoid excessive environmental damageand reduce unnecessary transportation costs. In addition, any othermeans to reduce equipment, material, and transportation costs isdesirable.

During clearwater drilling, water is pumped downhole through the drillstring to the drill bit, and is returned to the surface as a slurry,carrying cuttings and suspended solids. The slurry is then clarified andthe resulting clear water is recycled for use in further drilling. Atvarious stages of drilling, different drilling fluid compositions arerequired, and it is preferable that each fluid is similarly clarifiedand recycled to conserve resources and minimize environmental damage.

In typical drilling systems, used drilling fluid is clarified using acombination of screening, shakers, hydrocyclones, settling tanks,centrifuges, and flocculating agents. In systems incorporating primarilygravity-based settling means, a horizontal settling tank system may beused to provide a long flowpath for passage of the fluid, maximizingfluid retention time within the system and providing sufficientopportunity for solids to settle from the fluid. Once the fluid streamhas passed through the entire system, solids have settled at the bottomof the tank, and the drilling fluid has been sufficiently clarified thatit may be reused downhole.

Over time, settled solids build up in the tank compartments and must beremoved to maintain the quality of the clarified output fluid. Variousprior art systems employ solids conveying systems to transport solidsfrom the bottom of the settling compartments to the end or top of thetank for disposal exterior the system. For example, U.S. Pat. No.6,059,977 teaches the use of an auger system for conveying the solidsthrough the bottom of each tank compartment to an outlet port; U.S. Pat.No. 6,863,809 teaches pumping of solids through collection pipes to acentrifuge; and U.S. Pat. No. 6,391,195 teaches the use of a dragconveyor for transporting solids from the bottom of the solids tankupwardly to an outlet higher in elevation than the tank contents. Suchsolids removal systems involve mechanical parts which requiremaintenance and may also become clogged or jammed with solids duringuse. Moreover, the prior art tank systems are difficult to empty andclean following completion of drilling.

An additional objective of some fluid clarification systems is toconcentrate or thicken the solids stream for disposal directly on theground on-site. This generally requires a series of centrifuges todewater the solids stream, as selective removal of thickened solids fromthe settling tank is not possible. As centrifuges are expensive tooperate, requiring regular maintenance as well as consuming significantamounts of energy, it is desirable to minimize the use of centrifuges atthe drilling site by improving the concentration of the solids streamduring settling.

Further, in horizontal settling tank systems, solids accumulate in theinitial settling compartment more rapidly than in each subsequentsettling compartment. Moreover, the initial settling tank will generallyaccumulate larger, heavier solids that settle easily from the fluid,while the final compartment will generally accumulate finer solidparticles, at a slower rate. Thus, solids should generally be emptiedfrom the initial compartment more frequently than from subsequentcompartments. Such selective solids removal is not possible using thesolids conveying means of current horizontal settling tank systems.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate or mitigate at leastone disadvantage of previous fluid clarification systems. In a firstaspect of the invention, there is provided a fluid clarification systemcomprising one or more settling compartments, each settling compartmentcomprising: at least three walls; a base; and a solids outlet formedwithin the base, the base having inclined surfaces for guiding settledsolids to the solids outlet.

In an embodiment, each inclined surface extends towards the solidsoutlet at an angle from about 5 to about 60 degrees below horizontal.The walls of the compartments may also be inclined, for example,narrowing towards the base. The walls may be inclined between about 45and about 90 degrees below horizontal. In some embodiments, each wallmay be continuous with a base surface, with both inclined at the sameangle. The base may include a plurality of surfaces, with some inclined,and some vertical and/or horizontal.

In a further embodiment, the system further comprises a clear fluidcompartment continuous with the settling compartments for collectingclarified overflow fluid therefrom. The clear fluid compartment may beformed within the settling tank or may be external to the tank. If theclear fluid well is formed within the tank, the clear well is defined byat least one tank outer wall and at least one weir wall, as will bedescribed below.

In a embodiment particularly suitable for transport of the system, thesettling compartments are formed within a settling tank divided intosaid compartments by placement of one or more weir walls within the tanksuch that the at least three walls of each compartment include at leastone tank outer wall and at least one weir wall. The settling tank may befurther divided to form a clear well continuous with the settlingcompartments for collecting clarified overflow fluid therefrom, theclear well defined by at least two tank outer walls and at least oneweir wall. In a suitable embodiment, the weir walls extend from one tankside wall to the opposing tank side wall.

To facilitate a weir-like flow of fluid through the system, the weirwall between each successive settling compartment may be reduced inheight from the previous weir wall so as to direct overflow fluid tothrough the settling compartments in succession. In a suitableembodiment, the tank is divided by weir walls into three consecutivesettling compartments and a clear fluid well.

In a further embodiment, solids from each settling compartment aredirected through the respective solids outlet to a solids disposalsystem, which may include a centrifuge. A pump may be provided forpumping settled solids from each settling tank. The solids may be pumpedthrough a common conduit to the solids disposal system, or each solidsoutlet may be associated with a separate pump. The pumps may becontrolled independently or together. The system may further include acontrol system for operating the pump(s) as needed, for example based onthe weight and/or volume of solids in the tank.

Still further, the system may further include a flocculant reactiontrough positioned above, within, or otherwise contiguous with the firstsettling compartment, for delivering inflow feed and flocculating agentto the settling tank. The trough preferably includes baffles to promotemixing of slurry with flocculant. The baffles may be placed at an anglefrom 5 to 90 degrees from the direction of flow, and are fixed to thetrough sides or bottom. The baffles may extend past the trough midline.The trough may be sloped towards the compartment inlet.

In a further embodiment, a flocculant hydration and delivery system isprovided for delivering flocculant to the reaction trough and to thesolids stream collected from the solids outlets prior to furtherprocessing or centrifuging. The delivery system may further include acontrol system for regulating the rate of flocculant delivery to theflow trough.

In another embodiment, the system is of a size, shape, and weightsuitable for transport upon a skid or trailer, by road, air, water, oroff-road vehicle.

In a second aspect of the invention, there is provided a transportableclarifying system comprising a skid of suitable size for transport; andone or more settling compartments for mounting on the skid, eachsettling compartment defined by at least three walls and a base, thebase having inclined surfaces for guiding settled solids to a solidsoutlet.

In an embodiment of the invention, the skid is of suitable size fortransport by one or more of the following means: road, air, rail, water,or off road vehicle transport.

In a further embodiment, the system further comprises a solids removalsystem, wherein the solids removal system includes one or more pumpslocated on the skid beneath the inclined surface of one or more settlingtanks. One or more conduits for delivering pumped solids to a solidsdisposal system may also be present.

In a third aspect of the invention, there is provided a method forseparating solids from a fluid stream comprising the steps of directinga fluid stream into a first settling compartment, the settlingcompartment comprising a base having inclined surfaces for guidingsettled solids to a solids outlet; directing clarified overflow fluidout of the first settling compartment over a weir wall; and periodicallyremoving solids from the first settling compartment through the solidsoutlet.

In an embodiment, the method further comprises the step of addingflocculating agent to the fluid stream prior to directing the fluidstream into the first settling compartment.

In a specific embodiment, the flocculating agent is added to the fluidstream as the fluid stream passes through a flocculant reaction trough,the trough having baffles to promote mixing of the fluid stream with theflocculating agent.

The method may further comprise the step of directing the overflow fromthe first settling compartment into a second settling compartment tosettle further solids from the fluid stream.

In an embodiment, the settling compartment comprises at least threewalls, and the inclined surface of the base may extend towards thesolids outlet at an angle from about 5 to about 60 degrees belowhorizontal.

In a fourth aspect of the invention, there is provided an apparatus foruse in clarifying drilling fluids, the apparatus comprising one or moresettling compartments; each settling compartment defined by at leastthree walls and a base, the base having inclined surfaces convergingabout a solids outlet for guiding settled solids to the solids outlet.

In an embodiment of this aspect of the invention, the inclined surfacesextend toward the solids outlet at an angle between about 5 and about 60degrees below horizontal. Further, the compartment walls may beinclined, for example to narrow the compartment toward the compartmentbase.

In another embodiment, the apparatus comprises a clear fluid compartmentcontinuous with the settling compartments for collecting clarifiedoverflow fluid therefrom.

In an embodiment suitable for transport on a skid or trailer, thesettling compartments are formed within a settling tank divided intosaid compartments by placement of one or more weir walls within the tanksuch that the at least three walls of each compartment include at leastone tank outer wall and at least one weir wall.

In a suitable embodiment, the weir wall between each successive settlingcompartment is reduced in height from the previous weir wall so as todirect overflow fluid through the settling compartments in succession.One or more of the weir walls may be notched, angled, or have one ormore horizontally protruding weir plates to reduce the loading rate ofthe weir wall.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached Figures, wherein:

FIG. 1 is a top schematic view of a horizontal settling tank inaccordance with an embodiment of the invention;

FIG. 2 is a side cross-sectional schematic view of the tank shown inFIG. 1;

FIG. 3 is a cross-sectional schematic view of a single settlingcompartment in accordance with an embodiment of the invention takenacross line A-A in FIG. 1;

FIG. 4 is a perspective view of a clear well in accordance with anembodiment of the invention;

FIG. 5A is a top view of a tapered panel for use in assembling acompartment base in accordance with an embodiment of the invention;

FIG. 5B is a perspective view of an assembled compartment base inaccordance with an embodiment of the invention;

FIG. 6A is a top view of a polymer reaction tank in accordance with anembodiment of the invention; and

FIG. 6B is a side cross-sectional view of the polymer reaction tankshown in FIG. 6.

DETAILED DESCRIPTION

Generally, the present invention provides a method and system forclarifying fluids, particularly for clarifying drilling slurries.

With reference to FIGS. 1 and 2, in one embodiment of the invention, ahorizontal settling tank 100 is provided that is divided intocompartments. Slurry feed enters the tank at inlet 101, and passesthrough tank settling compartments 20, 30, and 40, to clarified fluidtank 50. Solids fall from the slurry in each tank settling compartment20, 30, and 40 and concentrate at the solids outlets 21, 31, and 41 ofeach respective compartment. Solids may be removed through each solidsoutlet as necessary to maintain the desired clarity of fluid withinclarified fluid tank 50. Tank compartments 20, 30, 40, and 50 areseparated from one another by weir and baffle systems such that fluidflows from tank inlet 101 to the clarified fluid tank 50 as describedbelow. The number of settling compartments may be varied from system tosystem as necessary. For example, in drilling operations in which largesolids as well as fine solids are suspended in the slurry, a longflowpath may be required to achieve sufficient separation.Alternatively, if only large, agglomerated solids are present, a tankwith only one compartment may be suitable to achieve sufficient fluidclarity.

The system may include a flow line trough 60 as shown in FIGS. 5 and 6,having baffles 61 to promote mixing of flocculating agent with theslurry feed. The baffles 61 provide some turbulence within the flow topromote mixing, without mechanically breaking up solids that havealready been agglomerated. This gentle mixing of slurry with flocculantwill permit a reduction in the amount of flocculant required, conservingmaterials and reducing costs.

The entire clarifying system may be transported on a trailer or skid,and the volume of the tank 100 may be maximized to the skid or trailersize permitted for road transport.

Division of Tank into Compartments by Weir Walls

With reference to FIG. 1, the horizontal settling system 100 shown isformed within a tank for ease of transport. The tank, having tank sidewalls 120, 130, and tank end walls 140, 150, is divided into threesettling compartments 20, 30, 40 and a clear fluid compartment 50 aswill be described below. The height of fluid within each successivecompartment 20, 30, 40, 50, is reduced from that of the previous tanksuch that fluid flows from inlet 101 through each of compartments 20,30, and 40, until it reaches clear fluid compartment 50. This isaccomplished by the use of weir walls 23, 33, 43 to separate each tankcompartment. Base portions having inclined surfaces and a solids outletare added or formed as part of each compartment

With reference to FIG. 3, settling compartment 30 is shown in end crosssection. The first settling compartment 20 is separated from the secondsettling compartment 30 by weir wall 23, which extends upwardly from thebase of tank side walls 120, 130 to a height H that is less than theheight of the tank sides. Thus, the height of the fluid contents of thefirst settling tank 20 will be determined by the height of the weir wall23.

With respect to the division between the second and third settling tanks30, 40, weir wall 33 extends from the base of the tank side walls to aheight I, where I<H. Thus, the height of the fluid contents of settlingtank 30 will be less than that of the first settling compartment 20, andoverflow fluid from settling compartment 20 will flow over weir wall 23into settling compartment 40.

Similarly, weir wall 43, which separates settling compartment 40 fromclear fluid compartment 50, is of a height J, where J<I<H. Thus, thefluid level within settling compartment 40 is lower than that insettling compartment 30, and overflow fluid from compartment 30 willflow over weir wall 33 into settling compartment 40. Overflow fromsettling tank 40 similarly flows over weir wall 43 into the clear fluidcompartment 50 as discussed below.

Alternatively, rather than using weir walls 23, 33, 43, having heightsH, I, J, one may wish to use weir walls of similar height to the tankwalls, with a portion of each weir wall notched to an appropriate depthto create the weir-like flow of overflow fluid from one settlingcompartment to the next. For example, the notched portions of the weirwalls would be of height H, I, J.

Weir Loading

In water treatment systems generally, it is desirable to reduce weirloading rates in order to reduce hydraulic gradients and minimizeturbulence within the system. In the present system, turbulence withinthe settling tanks should be minimized to avoid breaking up agglomeratedsolids and resuspending particulates within the fluid. Suitable methodsfor reducing weir loading rates include, for example, the use of notchedweir walls or attachment of one or more horizontally protruding weirplates to the weir wall. Both of these methods effectively increase thelength of the weir in relation to the amount of fluid flowing over theweir. It is understood that weir loading rates should generally bemaintained between 125 m³/day/m and 4000 m³/day/m. In the presentsystem, it is anticipated that weir loading rates of between 125m³/day/m and 1000 m³/day/m would be preferable.

Alternate Settling Tank Configurations

Many possible configurations of settling compartments may be designed inaccordance with the invention, as weir walls may be placed in anysuitable configuration within the tank 100 to customize the shape, size,and arrangement of the settling compartments. For example, in certaincircumstances it may be desirable to reduce the number of settlingcompartments to one or two compartments by using fewer weir walls; or toincrease the number of settling compartments, in which case additionalweir walls may be added to form various compartment shapes and flowpaths. Moreover, the compartments may be constructed of any suitableshape by adding baffles, tank walls, or weir walls as needed.

Specifically, in some circumstances a longer flowpath may be desirableto increase the retention time of the fluid within the system, promotingfurther settling of solids. Rather than transporting additional settlingcompartments to the site, a longer flowpath may be achieved within thesame overall system volume by creating a sinuous flowpath through thesettling compartments. For example, angled or notched weir walls may beplaced between the tank walls in alternating arrangement to direct flowover the first weir wall adjacent a first tank wall, while the nextsuccessive weir wall may be angled or notched in opposition to directflow to the opposing tank wall. Alternatively, a series of triangularcompartments may be created by diagonal placement of the weir wallswithin the tank, thereby creating a sinuous flowpath. Various additionalmeans for creating such a flowpath are possible and will be understoodby those skilled in the art upon reading the present disclosure.

In addition to construction of the present system by dividing a settlingtank into compartments, it is conceived that a system in accordance withthe invention may be composed of one or a series of individuallyconstructed settling compartments, with the overflow from each tank fedinto a successive compartment by adjacent placement of the compartments,or by use of a conduit system between the compartments. In sucharrangement, an overflow trough may be placed adjacent the weir wall ofthe settling compartment to collect overflow and deliver it to the nextcompartment.

Compartment Baffles

In addition to the weir walls 23, 33, and 43, baffles may be placedwithin each compartment to reduce turbulence caused by inflow of fluidto each compartment, and to enhance the settling characteristics of thesystem. As shown in FIGS. 1 through 3, baffles 26, 36, 46 are placedwithin each settling compartment. The baffles are preferably lengths ofsteel that are welded to the tank sides 120, 130, and extend from aheight slightly above the top of the weir walls to a depth significantlybelow the top of the weir walls. For most applications, it is preferablethat the baffles are placed between 50 mm to 1000 mm from the respectiveweir wall, however some experimentation may be required to determine theoptimum baffle size and placement for a given slurry composition andflow rate.

Clear Well

Once fluid has passed through the three settling compartments 20, 30,40, and solid has settled from the slurry, the resulting clarified fluidwill enter clarified fluid compartment 50, which is associated with asump for returning the fluid to the drilling operation. The sump shouldbe operated appropriately to ensure that the fluid level in clear well50 is maintained at a height lower than that of the adjacent settlingcompartment to prevent fluid backup into the settling compartments.

It should be understood that the clear well need not be a compartmentwithin the horizontal settling tank, in which case the overflow from thefinal settling tank may be collected by alternate means. For example,the clear well may simply be a conduit continuous with the uppermostportion of the final settling compartment. This configuration isparticularly preferable when a greater number of settling compartmentsor a longer flowpath is required to adequately settle solids from theslurry, as the clear well in such case would not take up valuabletransportable volume (eg. skid space), which would thus be available foruse in clarification.

Conversely, the horizontal settling tank may, in some circumstances,only require one settling compartment, in which case the clear well mayoccupy a large volume within the settling tank.

Solids Outlet

In each settling compartment, solids will fall from the slurry andcollect at the bottom of the settling compartments. As shown in FIG. 2,a solids outlet 21, 31, 41, is present within each compartment 20, 30,40, respectively, each of which is preferably associated with a pump toremove accumulated solids from the outlet. To facilitate concentrationof solids at the outlet, at least a portion of the compartment bases 21,31, 41, are inclined towards the solids outlet.

As shown in FIG. 5, the compartment bases are preferably assembled fromfour trapezoidal panels such that a central solids outlet will naturallybe created once the trapezoidal panels are joined as shown in FIG. 5B tocreate a substantially pyramidal base. In another embodiment, the solidsoutlet may be cut from a previously assembled compartment base. Theinverted pyramidal base shown in the Figures represents a pyramidal,conical, or hopper base configuration for the purpose of concentratingand directing solids toward the outlet. This structure has been found bythe inventors to sufficiently concentrate settled solids at the outlet,facilitating independent removal from each compartment as necessarywithout significantly disturbing the flow of fluid and settling ofsolids within the compartment. Other base configurations having inclinedsurfaces may be suitable for concentrating and directing solids towardthe outlet.

In certain circumstances it may be desirable to create a tank withcompartments having more than four sides (for example having a hexagonalor octagonal shape), in which case the pyramidal bottoms would beconstructed from an appropriate number of inclined bottom pieces.

It is also contemplated that the compartment base may be formed from onesheet of metal that is bent appropriately and welded along one or moreseams for attachment to the compartment walls. In further embodiments,each compartment wall may be formed with a portion of the base, simplybent to an appropriate angle, or the entire wall and base may extendtoward the solids outlet at a continuous angle. Such arrangements mayimprove concentration at the solids outlet, but may sacrifice necessarycompartment volume in certain applications, particularly if sizelimitations are imposed by the desired method of transportation. It istherefore anticipated that if the tank walls are to be angled towardsthe solids outlet, such angle be between 45 and 90 degrees fromhorizontal, and that the angle of the inclined bottom portions bebetween 5 and 60 degrees from horizontal in order to sufficientlyconcentrate solids at the solids outlet.

The panels forming the compartment bottoms are designed to providesufficient angle of incline to concentrate solids at the solids outlet,without sacrificing significant tank volume. In other words, it ispreferable to provide only a minimal slope of the bottom panel sectionsto retain maximal tank size, thereby maximizing fluid retention timewithin the tank. The angle of incline of the tank base is preferablybetween 5 and 60 degrees from horizontal, or between 95 and 150 degreesfrom vertical (ie. from compartment walls).

If appropriate, the areas beneath the tank sloped portions may be usedfor pumps, conduits, or storage and may be closed in by access doors andpanels if desired.

As stated above, solids may accumulate within each settling compartmentat different rates depending on the slurry fluid composition and flowrate. Using the present system, solids may be removed independently fromeach compartment and handled separately if desired. Alternatively,solids may be removed from each compartment and sent to a common conduitto be handled as a solids mixture. For example, solids from the firstsettling compartment may be large agglomerated solids that may simply bedeposited on-site without further treatment. By contrast, solids fromthe final settling compartment may be a flowable mixture of fine sandand fluid, which may benefit from further separation by a centrifuge.The present system permits a high degree of customization based on thecharacteristics of the slurry to be separated, and on the meansavailable for disposing of solid waste.

It is preferable that the pumps associated with each solids outlet beadjustable such that solids would be removed from each compartment at arate similar to the rate of solids accumulation in the respectivecompartment. This would enable a near-steady state of slurry fluidinflow, clarified fluid outflow, and solids output.

The solids outlet of each tank may also be used to empty the tankfollowing completion of drilling. This gravity-based drainage avoids thecostly transport and use of vacuum systems. Similarly, due to the slopedcompartment bottoms and location of the solids outlets, the tank may beeasily washed down and emptied prior to transport. As the present systemminimizes the use of moving parts such as conveyor systems and rakes,emptying and washdown are further simplified.

Flocculant Reaction Trough

With reference to FIGS. 6A and 6B, a flocculant reaction trough 60 isprovided continuous with the first settling compartment 20. The troughincludes baffles 61 to interrupt the flow of fluid and promote mixingwith flocculating agent (which may be polymer, coagulant, etc.), withoutcausing excessive turbulence that would destabilize the flocculant andbreak up agglomerated solids within the slurry. The gentle mixingprovided by the baffles 61 in the polymer reaction trough 60 increasescontact between slurry and flocculent, resulting in a reduction in thevolume or concentration of polymer required.

The polymer reaction trough is preferably sloped from its inlet end 62towards the outlet end 63, and preferably includes one or more baffles61. The baffles are preferably generally rectangular or triangular inshape and are placed at an angle from 75 to 90 degrees to the directionof flow. As shown in FIG. 6A, the baffles are preferably centered withinthe trough flow stream to ensure that slurry fluid will be appropriatelymixed. In an alternative baffle arrangement, baffles could extend fromthe trough sides past the trough midline M. Such baffles may extend intothe trough at any suitable angle.

In operation, slurry is pumped into the trough at trough inlet end 62,and flocculating agent/polymer is introduced to the reaction trough atinlet end 62. The polymer stream and slurry stream flow together towardsthe trough outflow end 63 and are mixed by contact with the bafflesystem. The outflow end 63 of the trough is continuous with tank inlet101, delivering slurry and polymer mixture to the first settlingcompartment 20. Inlet 101 of compartment 20, shown in FIG. 2, isextended below the trough bottom to direct slurry solids generallytowards the compartment bottom, minimizing surface turbulence within thesettling compartment 20. In addition, a baffle may be placed adjacentthe trough to further guide slurry solids towards the bottom of the tank20. An overflow weir is cut in the trough wall above the outlet torelieve any overflow.

As shown in FIG. 2, the reaction trough is preferably orientedhorizontally and located within the first settling compartment, withpolymer tanks 70, 71 placed adjacent the compartment for convenience.Alternatively, the reaction trough may be oriented vertically and placedwithin or adjacent the first settling tank. Many configurations ofreaction troughs are possible, however the intent is to provide a vesselhaving baffles to interrupt the flow of fluid, promoting gentle mixingof slurry with polymer, and delivering the mixture to the first settlingcompartment.

Preliminary testing by the inventor has shown that a 70-80% reduction inthe cost of polymer may be realized using the presently describedreaction trough, due to the improved efficiency in contact betweenslurry and polymer. Moreover, such reduction in polymer usage will alsoyield corresponding cost reductions in transporting and preparingpolymer for use. Accordingly, it is preferable that the concentrationand/or rate of release of polymer be regulated, monitored, and adjustedas needed during operation to fully realize the efficiencies describedabove.

Polymer tanks 70, 71 are used to mix and add polymer to flocculate ordewater slurry as needed. For example, a first tank 70 is preferablyused to hydrate polymer, while the second tank 71 stores the hydratedpolymer for delivery to the polymer trough or to the centrifuge feedline, if present. Any suitable flocculant system may be used with thepresent system.

Transport of System

The present horizontal settling tank system may be transported to urban,rural, or remote locations by means known in the art. For example, thecompact arrangement possible with the system facilitates customizationfor mounting upon a skid for transport by road, air-lift, rail, ship ortowing behind an off-road vehicle. Due to the additional materialhandling efficiencies of the system, such as reduced use of polymer andgreater concentration of solids, transportation costs may be furtherreduced.

In a preferred embodiment, a clarifying system in accordance with theinvention is mounted on a skid or trailer for transport and use. Due toroad limitations, such skids are generally approximately 40-53 feetlong, 8.3-12 feet wide, and 5.5-7.5 feet in height. To efficiently mountthe clarifying system upon the skid, while maximizing the fluid handlingcapabilities of the system, the system may be arranged as shown in FIGS.1 and 2. Polymer tanks 70, 71 are located at one end of the skid,adjacent the first settling compartment 20. The polymer reaction trough60 is placed adjacent the polymer tanks 70, 71 and over the firstsettling compartment 20, with outlet 101 beneath the desired fluid levelof the first compartment such that the slurry stream enters the firstcompartment below the surface of the compartment contents as discussedabove.

The inclined compartment bases provide additional space foraccommodating pumps and conduits, and/or may be used for storage. Theentire clarifying system may be mounted directly on a skid and operatedatop the skid with minimal bracing, avoiding the need for hoisting thesystem from the skid.

In certain embodiments, the system may include adjustable levellingmeans—for example, vertically adjustable weirs or a skid-levellingsystem to allow the user to balance the flow over the weir walls asnecessary.

EXAMPLE

The following example describes the general construction and testing ofa system constructed in accordance with an embodiment of the invention.

A skid-mounted horizontal settling tank (11.55 m long×2.74 m wide×1.70 mhigh) was divided by three weir walls into three settling compartments(3.04 m×2.74 m) and a clear fluid compartment (1.06 m×2.74 m), as shownin FIG. 1. A polymer hydrating system (1.37 m×2.74 m) was placedadjacent the first settling compartment, and a flocculant reactiontrough (0.60 m×2.74 m) was placed within the first settling compartmentas shown. The base of each settling compartment was created by joiningfour triangular panels into an inverted pyramid, with a solids outletcut from the lowermost portion of one of the triangular panels. Onceassembled, the base was 0.88 m high, and was attached to the walls at adepth of 0.82 m from the top of the tank. The triangular panelsextending from the tank side walls were inclined towards the solidsoutlet at an angle of approximately 32.5 degrees below horizontal, whilethe triangular panels extending from the weir walls were inclinedtowards the solids outlet at an angle of approximately 30 degrees belowhorizontal.

A steel pipe was cut at and angle and attached to each solids outlet toextend from the compartment base perpendicular to the skid. Each suchpipe was further connected to a solids discharge system. Upon pumping ofsolids from each compartment, flocculant was added and the solids streamwas further separated by centrifuge.

The weir walls used in the present system were constructed to depths ofapproximately 0.1 m, 0.2 m, and 0.3 m from the top of the tank, and werenot angled, notched, or otherwise customized to reduce the weir loadingrate. Two baffles were placed within the system, one within the secondsettling compartment adjacent the first weir wall, and one in the thirdsettling compartment adjacent the second weir wall. Baffles were spacedapart from the weir walls by approximately 0.3 m. Each baffle wasapproximately 0.5 m in height and extended across the width of thecompartment.

In operation, the system was tested up to 1.8 m³/min for approximately 3days of operation. Weir loading rates were calculated to be between 780m³/day/m and 950 m³/day/m. It was found during testing that the majorityof settling took place within the first settling compartment, and thesolids stream removed from the system was sufficiently concentrated thatprocessing by a single centrifuge with a processing rate ofapproximately 0.8-1.0 m³/min should be possible.

The above-described embodiments of the present invention are intended tobe examples only. Alterations, modifications and variations may beeffected to the particular embodiments by those of skill in the artwithout departing from the scope of the invention, which is definedsolely by the claims appended hereto.

1. A fluid clarification system for use in the treatment of a slurrystream, the clarification system comprising: two or more settlingcompartments for sequential passage and clarification of fluid, eachsettling compartment comprising at least three substantially verticalcompartment walls, each wall having upper, lower, and side edges, eachwall joined along its side edges to an adjacent wall to form acompartment having a first horizontal cross sectional area defined bythe lower edges of each joined compartment wall; and a compartment basecomprising a solids outlet having an opening within the compartment basefor gravimetrically discharging solids from the compartment base; and atleast three tapered panels, each panel attached to the lower edge ofeach compartment wall, and joined to an adjacent panel, the taperedpanels thereby converging about the opening so as to form a generallyinverted pyramidal shape for the compartment base of decreasinghorizontal cross sectional area towards the outlet, wherein the settlingcompartments are formed within a settling tank divided into saidcompartments by placement of one or more weir walls within the tank suchthat the at least three walls of each compartment comprise at least onetank outer wall and at least one weir wall, each weir wall extendingacross the tank and reduced in height from the tank outer walls so as todirect fluid over the weir wall and into a successive compartment, andfurther wherein one of the settling compartments comprises a baffleextending between opposing vertical compartment walls of said at leastthree vertical compartment walls, and said baffle being positionedadjacent a preceding weir wall to minimize turbulence of fluid enteringthe compartment, said baffle having a lower edge terminating above thelower edges of the opposing vertical compartment walls.
 2. The system asin claim 1 wherein the compartment walls are inclined so as to narrowthe compartment toward the compartment base.
 3. The system as in claim1, further comprising a clear fluid compartment continuous with thesettling compartments for collecting clarified overflow fluid therefrom.4. The system as in claim 1 wherein the tank is divided by weir wallsinto three consecutive settling compartments and a clear fluid well. 5.The system as in claim 1 further comprising a skid of suitable size fora particular mode of transport, wherein the settling compartments aremountable upon the skid for transport to and from a job site.
 6. Thesystem as in claim 5, further comprising a solids removal system,wherein the solids removal system includes one or more pumps located onthe skid beneath one or more settling tanks.
 7. The system as in claim6, further comprising one or more conduits for delivering pumped solidsto a solids disposal system.
 8. The system as in claim 7, wherein thesolids disposal system comprises a centrifuge.
 9. The system as in claim5 wherein the mode of transport is road, air, rail, water, or off roadvehicle transport.
 10. The system as in claim 1, further comprising asolids disposal system continuous with the solids outlet of eachsettling compartment.
 11. The system as in claim 10 wherein the solidsdisposal system comprises a centrifuge.
 12. The system as in claim 11wherein each compartment is generally triangular in horizontal crosssection.
 13. The system as in claim 10 wherein each solids outlet isemptied independently.
 14. The system as in claim 10 wherein the solidsoutlets of each settling compartment are connected in series by aconduit for delivering solids from the compartments to the solidsdisposal system.
 15. The system as in claim 1 further comprising apumping system for pumping concentrated solids from each settlingcompartment.
 16. The system as in claim 15, further comprising a controlsystem for controlling the operation of the pumping system.
 17. Thesystem as in claim 1 further comprising a flocculant reaction trough fordelivering inflow feed and flocculating agent to a first settlingcompartment.
 18. The system as in claim 17 further comprising a controlsystem for regulating the rate of flocculant delivery to the flocculanttrough.
 19. The system as in claim 17, wherein the flocculant reactiontrough comprises baffles to promote mixing of feed with flocculant. 20.The system as in claim 1 that is a size, shape, and weight suitable fortransport upon a skid or trailer.
 21. The system as in claim 1, whereinone or more of the weir walls are notched, angled, or have one or morehorizontally protruding weir plates to reduce the loading rate of theweir wall.
 22. The system as in claim 1, wherein each tapered panel ofthe compartment base extends towards the solids outlet at an anglebetween about 5 and about 60 degrees below horizontal.
 23. The system asin claim 1, wherein weir walls between successive settling compartmentsare alternately oriented within the tank so as to alternate thedirection of fluid flow from one compartment to the next, therebyincreasing fluid retention time within the tank.
 24. The system as inclaim 1, wherein weir walls between successive settling compartmentsdirect fluid flow in alternating directions with to establish a sinuousfluid flowpath through the tank.
 25. The system as in claim 1, whereinthe weir wall provides a weir loading rate of less than 1000 L/min/m 26.The system as in claim 1, wherein the system is operated at a linearflow rate greater than 1.6 m/min.
 27. The system as in claim 1 wherein:said baffle has an upper edge extending above an upper edge of thepreceding weir wall.
 28. An apparatus for use in clarifying drillingfluids, the apparatus comprising two or more settling compartments forsequential passage of fluid; each settling compartment defined by atleast three substantially vertical compartment walls and a pyramidalbase formed of at least three panels extending from a lower edge of eachcompartment wall and converging about a single, central solids outlet,for gravimetrically discharging solids from the pyramidal base, whereinthe settling compartments are formed within a settling tank divided intosaid compartments by placement of one or more weir walls within the tanksuch that the at least three walls of each compartment comprise at leastone tank outer wall and at least one weir wall, each weir wall extendingacross the tank and reduced in height from the tank outer walls so as todirect fluid over the weir wall and into a successive compartment, andfurther wherein one of the settling compartments comprises a baffleextending between opposing vertical compartment walls of said at leastthree vertical compartment walls, and said baffle being positionedadjacent a preceding weir wall to minimize turbulence of fluid enteringthe compartment, said baffle having a lower edge terminating above thelower edges of the opposing vertical compartment walls.
 29. Theapparatus as in claim 28, wherein the pyramidal base is formed oftapered panels inclined toward the solids outlet at an angle betweenabout 5 and about 60 degrees below horizontal.
 30. The apparatus as inclaim 28, further comprising a clear fluid compartment continuous withthe settling compartments for collecting clarified overflow fluidtherefrom.
 31. The apparatus as in claim 28, wherein one or more of theweir walls are notched, angled, or have one or more horizontallyprotruding weir plates to reduce the loading rate of the weir wall. 32.The apparatus as in claim 28 wherein: said baffle has an upper edgeextending above an upper edge of the preceding weir wall.